Fun fact! Cats actually do this to show affection, as it is a bonding ritual performed with other cats that rubs their scent on the other. Cats often see humans as just weirdly shaped cats, and thus don't realize that your center of gravity is different than theirs, and by trying to rub up against you in this manner that they're liable to make you trip. So basically, if your cat is "trying" to trip you, really they're just trying to say they love you, but in a uniquely cat way.